An example of a stock and flow diagram
The basics:
A stock is a noun, it can be measured at any given time and represents a quantity of something.
An inflow and outflow are verbs and are measured over the course of time.
Feedback is information about the stock and how the variables affect one another.
A common example of Stock and Flow diagrams is the following:
A stock is a noun, it can be measured at any given time and represents a quantity of something.
An inflow and outflow are verbs and are measured over the course of time.
Feedback is information about the stock and how the variables affect one another.
A common example of Stock and Flow diagrams is the following:
The bank account is the stock and always has a volume of cash, whether that is $3,109, $0, or $-52. The bank account will increase or decrease in size based on the amount of money going in (paychecks) or out (spending). The interest gained on the account will add to the size of the stock and is the feedback loop in this example.
On this example I added a blue "R" to the interest feedback loop to distinguish what kind of feedback the loop is. The "R" stands for reinforcing and indicates that the feedback will generate more input for a stock based on the amount already there.
Defining the types of feedback loops:
Balancing Feedback: Equilibrating or goal-seeking structures in systems and are both sources of stability and sources of resistance to change.
Reinforcing Feedback: Self-enhancing, leading to exponential growth or to runaway collapses over time. They are found whenever a stock has the capacity to reinforce or reproduce itself.
(Source: Meadows, Donella H., and Diana Wright. Thinking in Systems: A Primer. White River Junction, VT: Chelsea Green Pub., 2008. 28-32. Print.)
On this example I added a blue "R" to the interest feedback loop to distinguish what kind of feedback the loop is. The "R" stands for reinforcing and indicates that the feedback will generate more input for a stock based on the amount already there.
Defining the types of feedback loops:
Balancing Feedback: Equilibrating or goal-seeking structures in systems and are both sources of stability and sources of resistance to change.
Reinforcing Feedback: Self-enhancing, leading to exponential growth or to runaway collapses over time. They are found whenever a stock has the capacity to reinforce or reproduce itself.
(Source: Meadows, Donella H., and Diana Wright. Thinking in Systems: A Primer. White River Junction, VT: Chelsea Green Pub., 2008. 28-32. Print.)